Mr Graham added: “So could I ask your guidance how to stay as respectful as possible in this place and on social media and what can be done to help the security of our staff in our constituencies?”

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Mr Bercow said “that behaviour was despicable and should be condemned unreservedly”, adding he was “sorry for what ghastly experience his staffer has undergone”.

On the point about respect, he said: “May I suggest these are difficult watchwords, none of us observes them unfailingly, including me, but my watchwords in terms of how we all conduct ourselves are this; political difference, personal amiability.”

He gave the example of veteran Tory MP Ken Clarke, the Father of the House, who he said is able to “express a robust view but to play the ball rather than the man or woman”.

The Speaker added that people who make threats or use violence because of a disagreement of view “need to be shown that is not acceptable, and where they break the law the full force will be applied to them”.